It has been known for some time that the yield of hydrocarbons, such as gas and petroleum, from wells can be increased by fracturing the formation so as to stimulate the flow of hydrocarbons into the well. Various formation fracturing procedures have been proposed and many now are in use. Among these procedures are treatments with various chemicals (usually acids in aqueous solutions), hydraulic fracturing in which liquids are injected under high pressure (usually with propping agents), explosive methods in which explosives are detonated within a formation to effect mechanical fracture, and combinations of the above procedures.
A combustion method designed to stimulate a well through mechanical fracturing is known as controlled pulse fracturing (CPF) or high energy gas fracturing. A good description of this method appears in an article by Cuderman, J. F., entitled "High Energy Gas Fracturing Development," Sandia National Laboratories, SAND 83-2137, October 1983. Using this method enables the multiple fracturing of a formation or reservoir in a radial manner which increases the possibility of contacting natural fractures. Unfortunately, these radial fractures often do not penetrate deeply enough into the formation.
A hydraulic fracturing method designed to control fracture trajectories in a formation penetrated by two closely-spaced wells is known as sequential hydraulic fracturing. In sequential hydraulic fracturing, the direction that a hydraulic fracture will propagate is controlled by altering the local in-situ stress distribution in the vicinity of the first wellbore. By this method, a hydraulic fracturing operation is conducted at the first wellbore wherein a hydraulic pressure is applied to the formation sufficient to cause a hydraulic fracture to form perpendicular to the least principal in-situ stress. While maintaining pressure in this first hydraulic fracture, a second hydraulic fracture is initiated in the second wellbore. This second hydraulic fracture, due to the alteration of the local in-situ stresses by the first hydraulic fracture will initiate at an angle, possibly perpendicular, to the first hydraulic fracture. In propagating, this second hydraulic fracture then has the potential of intersecting natural fractures not contacted by the first hydraulic fracture, thereby significantly improving the potential for enhanced hydrocarbon production and cumulative recovery.
Therefore, what is needed is a method which combines both CPF and sequential hydraulic fracturing techniques in order to extend these controlled pulse fractures so as to permit removal of increased amounts of natural resources from an underground formation. Practicing the present invention will allow for the creation of fracture extensions emanating from CPF induced radial fractures so as to connect with natural fractures and allow for the production of increased amounts of natural resources from a formation. Even in the absence of natural fractures, productivity will be increased due to the additional multiple fracture surface areas created by practicing this invention.